ABSTRACT

Tam Giang Lagoon, one of the largest lagoons in Asia, has an area of 22,000
ha and stretches for more than 60 km. Current aquaculture methods are mainly
fish ponds, net enclosures and cage systems. Ponds are more commonly used for
extensive, improved-extensive and semi-intensive types of culture, and in 1998,
covered an area of about 1,980 ha. Aquaculture is being developed in the lagoon
to overcome the depletion of natural aquatic resources and to satisfy the demand
of the increasing population for aquatic products. The local government considers
it an alternative measure to improve lagoon-dwellers' income and a means of
reducing random exploitation of the lagoon's resources. As a consequence of
the increased exploitation, environmental conditions have deteriorated. Some
water quality parameters have exceeded their permissible limits. Diseases have
been reported in four major cultured species (i.e., seaweed (Gracilaria sp.),
shrimp, crab and fish) with high risk and frequency. Two disease epidemics broke
out in 1995 and 1998, causing great losses to aquaculturists. The diseases resulted
in an enhancement of the role played by the Aquatic Animal Hygiene Inspection
and Veterinary Office of the Department of Fisheries in developing new mechanisms
and strategies for the management of aquatic animal health in the lagoon. This
paper also presents a proposal for a "Tam Giang Lagoon Aquatic Systems
Health Assessment," which is based on research results from the International
Development Research Centre of Canada (IDRC)-sponsored project "Management
of Biological Resources in Tam Giang Lagoon," as well as on input provided
by specialists from the Network of Aquaculture Centres in Asia-Pacific (NACA).

INTRODUCTION

Tam Giang Lagoon (see Figure 1), which runs along the coast of Thua Thien Hue
Province, Vietnam, has an area of 22,000 ha and a length of more than 60 km.
On its eastern side, the lagoon is separated from the sea by sandy dunes with
two openings, Thuan An and Tu Hien. On the western side of the lagoon are rice
fields and river estuaries. The area is unique in terms of landscape and biological
resources. Communities settled there to exploit the lagoon's biological resources
and farm on the sandy land at its edge.

Because of increasing population pressure and a decrease in aquatic resources,
government officials consider aquaculture as an alternative means of improving
villagers' income and reducing exploitation pressure on the lagoon. As a result,
aquaculture has recently developed so rapidly that it is having a strong impact
on attempts to promote a sustainable aquaculture production system in the lagoon
area.

Figure 1. Map of Tam Giang Lagoon.

FACTORS AFFECTING AQUACULTURE DEVELOPMENT

Tam Giang Lagoon mixes with the sea through the two openings on the eastern
side. The lagoon also receives water from many rivers, such as the Huong, Bo,
Dai, O Lau and Truoi. Thanks to this unique topography, the lagoon has a mixture
of fresh and salt water that makes the changes in its salinity both seasonally
and spatially regular. This creates a typically brackishwater environment with
valuable resources and a high potential for aquaculture.

The average depth of the lagoon is 2 m, although along its length there runs
a channel 3 to 4 m deep. Thuan An Estuary is deepest, at more than 7 m. Therefore,
the salinity and characteristics are favourable for the construction of aquaculture
ponds and net enclosures in most parts of the lagoon.

AQUACULTURE DEVELOPMENT

The first aquaculture activities in Tam Giang Lagoon began with seaweed cultivation
in 1977. Shrimp culture began in the early 1990s, and from 1990 to 1993, the
area of shrimp ponds increased from 42 to 437 ha. Meanwhile, the area under
seaweed cultivation increased from 226 to 357 ha. The total aquaculture area
in the lagoon reached 1,000 ha in 1995 (Phap 1996).

Present aquaculture methods involve mainly ponds, net enclosures and cages.
Ponds are more common for the following systems: extensive, improved-extensive
and semi-intensive. The area of production and the aquaculture patterns in the
lagoon in 1996 are presented in Table 1 and Figure 2 (Phap 1996).

Table 1. Types of aquaculture and areas covered in Tam Giang Lagoon.

During the 1998 culture season, the area of net enclosure in Phu Tan Commune
alone (where most of the aquaculture activity is concentrated) was 413.5 ha.
Although this does not present a full picture of the aquaculture boom in the
lagoon, it does reflect the significant rate of increase.

Figure 2. Aquaculture production in Tam Giang Lagoon, 1992-96.

Aquaculture is regarded as a pilot scheme investigating the economic potential
for fisheries development in Thua Thien Hue. The Department of Fisheries in
Thua Thien Hue promotes semi-intensive culture in which villagers include aquaculture
as part of their livelihood portfolio and state-run companies supply seed and
technical support. This is the official strategy for aquaculture development
in Thua Thien Hue Province (Phap 1996).

In the past five years, basic aquaculture techniques, acquired from training
courses held at the Fishery Extension Centre, Phu Tan, have enabled the lagoon
fishers to experiment and learn from other experienced aquaculturists. Step
by step, they are developing their own aquaculture practices that are characterised
by low stocking density and polyculture. Polyculture seems to be more sustainable
than monoculture, as it reduces the risk of losing the whole crop due to disease.
Common polyculture patterns include: shrimp (Penaeus monodon)/crab (Scylla serrata)/
fish (Siganus guttatus)/seaweed (Gracilaria tenuistipitata); shrimp/ seaweed
and shrimp/crab/fish. Grouper and grass carp (Ctenopharyngodon idellus) are
cultured in cages.

This flexible approach is more appropriate to the environmental conditions
of the Tam Giang ecosystem and to the management and investment capacities of
local people. This runs counter to previous aquaculture development (semi-intensive
and monoculture) that was applied by state-run companies. Low intensity polyculture
has resulted in increased economic benefits, because investments for seed and
feed are low, no improved techniques are required, product quality is good and
the price obtained for the product is higher than in high-density culture.

Meanwhile, aquaculture companies that relied on more intensive cultivation
methods have had to abandon their ponds or rent them to fisherfolk; these companies
are no longer involved in aquaculture development in Tam Giang Lagoon. However,
aquaculture production in the lagoon is still regarded as unstable, and further
research is required to address the associated problems.

THE LIFE OF AQUACULTURE COMMUNITIES

Approximately 220,000 people in 38,000 households, or about 20% of the population
of the province, live directly around the lagoon. The population is increasing
at a rate of 3.1% per year. Families in villages around the edge of the lagoon
that depend on agriculture as their main livelihood activity have the lowest
income in their community, while families who have adopted aquaculture have
higher incomes (Newkirk 1995).

Before 1970, the total fish catch in the lagoon was about 3,600 mt/yr; however,
since 1980, production has been around 2,000 mt/yr. The number of persons engaged
in fishing has increased rapidly, from 66,000 in 1980 to 90,000 in 1993. The
amount of fishing gear used has also increased; 13 types of fishing gear are
in use, including fishing corrals, fixed lift nets and bottom nets, all in high
density. Electro-fishing gear is also becoming commonplace.

High fishing intensity has resulted in the depletion of the lagoon's resources
and increased the difficulties of fisherfolk. To improve the situation, aquaculture
has been accepted by the fisherfolk and is considered by local government as
an alternative source of income, as well as contributing to reducing degradation
of the lagoon's aquatic resources. Aquaculture brings greater income, which
helps improve the life of the fisherfolk. For example, in Phu Tan Commune, changes
have resulted in an improvement of infrastructure, and most families now have
brick houses with modern conveniences. Community health care and education are
also improving; the number of malnourished children is decreasing and over 80%
of the children attend school.

Nevertheless, aquaculture demands a high initial investment, and a high risk
of disease outbreaks may result in losses. Therefore, the poor fisherfolk, who
are mostly migratory fishers, cannot get involved, while their natural fishing
grounds are becoming more confined This widens the gap between the more wealthy,
the mobile fishers and the poor in these communities.

EMERGING DISEASE PROBLEMS

The Aquatic Animal Health Situation

Aquaculture in Tam Giang Lagoon is generally regarded as a risky venture associated
with high mortalities from disease. Diseases are common in the lagoon, and all
four groups of cultured species (seaweed, shrimp, crab and fish) have been affected.

In 1985 "colourless" disease appeared in Gracilaria. The local fishers
call it "white canopy" disease, the tips of the fronds becoming white
and the thallus perishing. Meanwhile, some fish species living in the Gracilaria
ponds, such as mullets and rabbitfish, suffered from ulcers.

Recently, at the Quang Thai Commune, a research site of the Tam Giang Project,
26 households were supported with capital from the project to develop grasscarp
cage culture; however, after. months of rearing the fish, 80% of the cages suffered
100% mortality from "red spot" disease. So far, 16 diseases of aquatic
animals have been recorded in Tam Giang Lagoon (Table 3).
In the Hue area, there are eight hatcheries for shrimp fry production (one state-run,
seven private) and 28 nursing units. The average number of postlarvae (PL15)
produced each year is about 20 million, meeting half of the local demand.

The common diseases in fry are luminescent disease, carapace deformation, red
spot and external fouling. Interventions applied by fisherfolk to reduce the
impact of disease on affected animals consist of changing the water to improve
water quality and providing enough food to help the animals overcome the disease.
Some fry producers have used antibiotics and chemicals for treatment of disease
(Table 4).

Aquatic animal diseases have been recognised since 1994. They tend to spread
over a large area of the lagoon in March, April, July and August of each year.
There are no official statistics on the economic impact of disease; however,
data from the Department of Fisheries suggest that the impact has been severe.
For example, during the 1995 shrimp disease epidemic, 300 million fry and 900
million grow-out animals died. This resulted in huge capital losses for the
farmers, and many have been unable to repay their bank loans. A survey showed
that one household lost all its capital when it invested 38 million Vietnamese
Dong (VND) (1 US$= 14,000 VND) after stocking 20,000 PL15 in a 5,000 m2 pond
in 1998. Due to disease, another household received only 15 million VND in returns
after investing 52 million in a 3,000 m2 pond (Anon. 1999).

Aquatic Animal Health Management

The Aquatic Animal Health Inspection Office (AAHIO), Department of Fisheries,
has responsibility for managing the health of cultured species in the whole
lagoon. The staff of the AAHIO consists of five people, one of whom is responsible
for carrying out laboratory work. The other staff conduct monthly field visits
to inspect the health of cultured animals, to provide the fisherfolk with guidance
to improve pond conditions before stocking, and to teach them the basic indicators
used to identify healthy fry. The AAHIO keeps in regular touch with the fisherfolk
to assess aquaculture activities and to collect samples of diseased animals.

Fry production is strictly controlled by the AAHIO. All production units require
health certificates and production licenses. The AAHIO also organises training
courses to teach the fisherfolk how to protect their cultured animals from becoming
infected (Anon. 1999).

Table 4. Antibiotics and chemicals used in treatment of fry diseases (source:
producers).

In the event of an epidemic, the AAHIO must report the situation and the resulting
losses to the Provincial Peoples Committee (PPC). Based on this report, the
chairman of the PPC provides advice and recommends solutions to manage the problem,
and provides support to producers who suffer great losses. For example, in the
epidemics of 1995 and 1997, the banks extended repayment deadlines and granted
low-interest loans (Anon. 1999).

Research on aquatic animal diseases is a new area for the University of Hue
and the AAHIO. Initial research conducted by the Department of Biology (Hue
University of Sciences) and the Department of Fishery (Hue Agriculture and Forestry)
concentrated only on diseases caused by protozoan parasites and fungi, such
as Fusarium spp. and Lagenidium spp.

Even though a co-operative programme is in place between the Department of
Fisheries and Hue University to study aquatic animal diseases, there are still
no effective measures for controlling diseases in aquaculture. Therefore, the
office has adopted the following animal health management (Anon. 1999):

Clean the rearing ponds before stocking fry and maintain the cleanliness
of the water to minimise diseases.

Carry out health checks of the fry before stocking in the ponds.

Conduct inspections of the production process and conduct farmer-based participatory
training to help farmers recognise diseases and devise management strategies.

Recommend that the PPC set up insurance funds aimed at supporting culture
units or fisherfolk suffering serious hardship.

One of the objectives of the Tam Giang Project is to develop methods of sustainable
aquaculture production by addressing technological, organisational and regulatory
issues (Newkirk 1995). From 1998 to 1999, the IDRC-supported Tam Giang Project
undertook two research activities, implemented at Phu Tan Commune, related
to improvement of the culture pond water of the lagoon: (i) trials on raising
monosex Tilapia in polluted ponds, and (ii) a study of preliminary impacts
of improved-extensive culture on the natural environment of the pond. Initial
results show that:

In the pond with improved-extensive farming, parameters such as pH, dissolved
oxygen and biological oxygen demand all exceeded levels that could result in
stress-associated mortalities.

The environment of organically polluted ponds is remarkably improved after
tilapia are stocked, and it is then possible for shrimp to be reared in the
system. Using this method for cleaning the pond environment, some aquaculturists
achieved a shrimp harvest in 1999 valued at around 30 million VND/pond (Hong
1999).

These results uphold the local aquaculturists' perception of the importance
of maintaining adequate water quality to help reduce losses from diseases that
are exacerbated by stress.

APPROACH TO AQUATIC ANIMAL HEALTH ASSESSMENT IN TAM GIANG LAGOON

Tam Giang Lagoon has a close relationship with the sea and the land. Its
biological and physical characteristics have created a unique brackishwater
ecosystem with a diverse range of resources, supporting a large population
around the lagoon.

With rapid development, the whole area over 2 m in depth will soon become
an aquaculture area, and this will increase the income of the local people,
contributing to poverty alleviation in lagoon fishing communities. However,
three main constraints have been identified: lack of capital, lack of good
fry and occurrence of disease. The latter is considered to be the biggest
constraint, for which there is still no solution. In order to solve this problem,
the "Tam Giang Lagoon Aquatic System Health Assessment Project"
has been proposed. The specific objectives of the project are:

To identify the current problems in the Tam Giang Lagoon and assess their
social and economic impacts.

To determine strategies to reduce identified impacts.

To identify and assess current problems, the aquaculture production systems
in two different areas of the lagoon will be investigated, as well as the
range of people involved in using these systems for their livelihoods. The
areas are: Phu Tan, where aquaculture is well developed, and Quang Thai, where
the people are poorer and aquaculture is a recent introduction. The species
cultured, number of households involved and disease problems encountered are
shown in Table 5.

This comparative analysis between people and locations, where aquaculture
is in different stages of development, will enable lessons from areas with
more experienced farmers to be applied in new locations.

METHODS

Survey team

The survey will be undertaken by a research team from the Tam Giang Project:
- 7 people from the project

Prompt or list of key points.
Train farmers to fill in the key points.
Semi-structured questionnaires.

3. Observation
Based on key informant interviews, if the farmers find a disease problem,
then researchers will visit the site, observe the situation and carry out
field-environmental and laboratory investigations.

Preliminary key points to be addressed include:

What are the problems?

What are the social and economic impacts of these problems?

What do they do about the problem?

Institutional analysis

An institutional analysis will be carried out to determine the different
institutions involved and their current and possible future roles in aquatic
animal health management, as well as the training needs at the different levels
(village, commune, district and province). Extension capabilities and the
support available to farmers will also be evaluated. The roles and inputs
of suppliers of seed and bankers as possible sources of management intervention
will also be defined.

Expected outcome and follow up

The outcome from this work is expected to include:

An assessment of current aquatic animal health problems and their social
and economic impacts. Particular attention will be given to the potential impact
of aquaculture on poverty alleviation.

An institutional analysis and needs assessment will allow the roles of different
"actors" to be identified and areas for strengthening, from farmer
to provincial government level, to be identified. A training-needs analysis,
based on a clear understanding of current and future farmer problems, will also
help to identify training needs and how these might be fulfilled.

Capacity building, institutional arrangements, training needs and other interventions
will be identified.

A project proposal to put health in the perspective of system management
will be developed.

Overall, the activity will contribute to the sustainable management of aquaculture
resources in the lagoon for the livelihood of the people involved.